I would like to roll out rdrive to multiple workstations that then run a script that backs up the local HDD to a network drive.

This I can do with ease, and it works really well when creating a new single file every time!

However, I would like to enable differential or incremental backups so that i could potentially restore back to a certain date. This I can also do and it works well.

My issue is how do I limit the amount of space each user takes up on the network drive? I have set the Imaging mode to use backup sets, set the quota to say 10Gb and the number of sets to 1, but it just carries on backing up past 10gb and keeps going. The initial image size is 6Gb, the differentail images are around the 512mb size.

The problem is that you have to create two tasks: one for a full image, the other for incremental backups. See R-Drive Image -> Scheduled Actions, Command Line Operations, and Scripting -> Backup Sets.
Just enter your values.
Just remember: R-Drive Image always keeps at least one backup set for not loosing the data.